1. Field of the Invention
This invention relates to an improved process for making carboxylic acids by ozonolysis of a compound having at least one olefinic bond and subsequent reaction of the ozonolysis products with oxygen in the presence of a solid phase manganese catalyst.
2. Description of the Related Art
The general chemical course of the reactions involved in the process according to this invention is well known. For example, it is well known that azelaic and pelargonic acids can be made by ozonolysis of oleic acid as described in U.S. Pat. No. 2,813,113, the entire contents of which are incorporated herein by reference. In general, the process involves the ozonization of olefinic compound to form a mixture of ozonides, treatment of the ozonides with an oxidizing agent such as hydrogen peroxide or oxygen to form a mixture of oxidation products, hereafter abbreviated as MOP. MOP is comprised of carboxylic acids and other carbonyl-containing species such as aldehydes and ketones. The combined concentration of aldehydes and ketones is expressed as a carbonyl value which is abbreviated as COV and has the units parts per million (ppm). The COV value of the oxidation products of the MOP must be reduced because the end users of the products of the process according to the invention have found that aldehydes and ketones interfere with subsequent reactions and/or produce color in the final products. For example, the process according to the invention is especially suitable for the manufacture of azelaic acid (1,9-nonanedicarboxylic acid). Azelaic acid is an important ingredient in such items as modified polyester fibers for apparel and carpeting, and engineering plastics. It is also used in urethane elastomers, polyester films and adhesives, plasticizers, and synthetic lubricants. Manufacturers of such products have found that small amounts of aldehydes and ketones can result in discoloration of the final products. It is very important, therefore, to reduce the amount of aldehydes and ketones present in azelaic acid to a minimum or eliminate them altogether.
The COV of the oxidation product mixture can be reduced to a minimum by further reaction with oxygen and preferably with oxygen in the presence of a transition metal ion catalyst such as cobalt and manganese. The COV reduction process will typically reduce the COV from a value of, for example, 6300 ppm to a value of 5800 ppm in 5 hours in the presence of oxygen and without manganese catalyst and from 6300 ppm to 2700 ppm in 5 hours with oxygen and with manganese catalyst. Prior to the present invention, the principal difficulty encountered with the use of manganese catalysts was that the manganese ion was typically used at a concentration of 1500 ppm and the soluble manganese ion invariably ended up in effluent waste streams. Since state and federal regulatory standards for manganese levels in effluent streams are being set at progressively lower values, the presence of the manganese ion in waste streams can present a major environmental problem.
The process according to the invention eliminates the problem of waste stream contamination by the use of manganese catalysts wherein the manganese ion is immobilized in the COV reduction process. Preferably, the manganese can be immobilized by incorporating it into a solid phase system such as an manganese-exchanged zeolite wherein other metal ions such as Na.sup.+ have been exchanged by Mn.sup.+2. A solid phase manganese catalyst such as Mn.sup.+2 -exchanged zeolite can be recycled repeatedly into the COV reduction process thereby reducing catalyst cost and eliminating manganese from the process effluent.